Heat exchange systems have been used for different purposes, such as warming water used for domestic, commercial, or industrial purposes. Designers of heat exchange systems have faced many challenges such as limitations on the size of the heat exchanger. Additionally, there is a need for the warmed fluid to exit the system at a consistent temperature. Managing the temperature of the cooled fluid leaving the system is also a challenge facing heat exchange systems due to efficiency and regulatory concerns.
Changes in the demand for heating require that heat exchange systems be able to provide vastly different amounts of heating, which can lead to substantial temperature changes in the output of the warmed fluid. Conventional methods of stabilizing the output temperature of the warmed fluid often rely on adjusting the flow rate of the fluid to be cooled. Although this approach may reduce the variability of the warmed fluid output temperature, the cooled fluid temperature leaving the heat exchanger can vary drastically.
Conventional systems used to heat water often have two fluid circuits. Typically water to be heated circulates in the first fluid circuit in a liquid state while steam circulates in the second fluid circuit at temperatures that are often above the boiling point of water. Both circuits meet at a heat exchanger unit where the cool water is warmed by flowing over thermally conductive conduits containing the high temperature steam. The water exits the heat exchanger in a heated state, and if the demand for hot water increases, the flow rate of the hot water vapor is simply increased.
In conventional systems, the temperature of the heated water at the outlet varies based on the outgoing water flow rate variations and/or according to incoming water temperature variations. As a result of the variable flow rate through the heat exchanger, the quantity of energy transmitted cannot be precisely controlled causing the temperature of the output water to vary. Additionally, the high temperature of the steam limits control, but is needed for high usage situations. In low usage situations, the steam will often warm the water up to a temperature beyond that which is desired.
A varying output temperature of the cooled fluid from the heat exchanger can reduce the efficiency of the energy exchange since energy remaining in the cooled fluid is often wasted. There are also many instances where there are requirements and regulations on the temperature of the cooled fluid leaving the heat exchanger. In systems where the cooled fluid is not returned to its source for reheating, the cooled fluid is often dumped into a sewer system or waterway. In addition to being inefficient, dumped fluids often must be below a specified temperature to avoid damaging sewer systems or to avoid causing thermal pollution that can lead to problems such as algae blooms.
In addition to the other problems associated with heat exchangers, floor space is often at a premium in modern mechanical rooms so it is desirable to have a heat exchanger with a minimal footprint. The cost difference in using a system with a small 1.75 square yard footprint versus having to stack multiple regular horizontal exchangers can be thousands of dollars. Thus, it is desirable to provide a vertically oriented heated exchanger with a minimal footprint. Additionally, retrofit applications require heat exchangers to be placed in small areas. Large, bulky 40 to 50 year old exchangers may be at the end of their useful life. Many times a facility is built up around these failing units and replacing them with a similarly sized unit would entail major demolition. Vertical exchangers can be wheeled through a doorway and they can be piped up with the existing unit in place, causing minimal downtime. Sometimes the existing unit is encapsulated and left in place.
Attempts have been made to solve some of these problems, such as in U.S. Pat. No. 6,857,467 issued to Lach, the contents of which are herein incorporated by reference. The Lach patent claims to disclose a “heat exchange system . . . used for heating a first fluid with a second fluid [using] . . . a flooded heat exchanger . . . capable of being flooded in a determined proportion [and] . . . includes a second fluid circuit control valve . . . for controlling the flow rate of the second fluid . . . whereby the proportion of the heat exchanger which is flooded . . . can be selectively calibrated. The heat exchange system also includes a first fluid pre-heating device . . . for partly pre-heating the first fluid before it is heated by the second fluid, whereby the first fluid temperature at the first fluid circuit downstream end will be stabilized.” Although the Lach patent attempts to improve the temperature stability of a first fluid leaving the heat exchanger, the Lach patent fails to provide a mechanism for stabilizing and reducing the output temperature of the cooled fluid.
Semi-instantaneous water heaters attempt to stabilize the output temperature of water heaters by having small mixing tanks in which water delivered from the heat exchanger is blended with water in the vessel. U.S. Pat. No. 4,278,069 issued to Clark discloses an example of a semi-instantaneous water heater, the contents of which are herein incorporated by reference. While it is possible to obtain temperature control of the warmed fluid in semi-instantaneous water heaters, the output temperature of the cooled fluid is uncontrolled.
Although designs by Lach and Clark have attempted to solve some of the problems associated with heat exchangers, all of these problems have yet to be fully addressed. Objects of the present invention include providing a fluid heater with a low installation cost, providing a more efficient heat transfer from steam, providing a heat exchanger that requires less physical space, providing a heat exchanger that does not require a condensate pump, a vacuum breaker, or a pressure regulating valve station, controlling the temperature of the liquid leaving the heat exchanger within ±3° F., and decreasing the temperature of the steam condensate leaving the heat exchanger.